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    <title>Document</title>
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    <div id="hello">1</div>
    <script>

        // isNaN:判断一个变量是不是一个非数字 ，如果是一个非数字 那么返还true 否则就是false
        // var str = "fdad";
        // console.log(!isNaN(str));

        // var arr = ["张三","李四","王五"];
        // console.log(arr.indexOf("李四1"));
        // includes 判断数组里是否包含某个值，如果包含就返还true 否则就返还false；
        // console.log(arr.includes("43243"));
// var ele = document.getElementsById("hello");
// console.log(ele);
    </script>
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